1. Field of the Invention
The present invention relates to a combined cycle power plant in which a gas turbine plant and a steam turbine plant are combined, and to a cooling steam supply method for a gas turbine in operation thereof.
2. Description of the Prior Art
A combined cycle power plant is a power system in which a gas turbine plant and a steam turbine plant are combined, wherein a gas turbine takes charge of a high temperature section of thermal energy and a steam turbine takes charge of a low temperature section thereof. Therefore, the thermal energy is recovered for an effective use thereof and this power system is now being paid a high amount of attention.
In the combined cycle power plant research and development are being carried out aiming at a higher temperature gas turbine as one means for enhancing the efficiency.
On the other hand, in order to attain such a higher temperature, improvement of the cooling system which takes account of heat resisting ability of turbine structural elements must be pursued. As a result of various trials and errors, a steam cooled system which uses steam as the cooling medium, instead of a prior art use of compressed air, is now in progress.
One example thereof is the Japanese laid-open patent application No. Hei 05 (1993)-163960, wherein a cooling steam is obtained from intermediate pressure steam of a waste heat recovery boiler. However, a sufficient volume of steam is not obtainable which results in difficulty in achieving a stable and secure cooling.
Thus, as a further progress thereafter, in order to achieve a sufficient volume and a stable cooling, a cooling system using exhaust steam from a high pressure steam turbine as the cooling steam is now being developed.
In the prior art steam cooled system as mentioned above, progress has been made from the system using intermediate pressure steam as the cooling medium to that using high pressure exhaust steam, and thus the practicality has been enhanced further. However, the high pressure exhaust steam is of a high temperature at the same time, hence a gas turbine high temperature portion (which is a portion to be cooled) must be made of a selected material which can resist such a high temperature.
A high temperature resistible material, being required to be of properties necessary for that material, becomes very expensive. Furthermore, in case of a turbine disc among others for example, there is a large difficulty in obtaining an appropriate material therefor within limited conditions of price and the like, which leads to a serious problem in the design and manufacture of the plant.
In view of the problems in the prior art, it is an object of the present invention to provide a combined cycle power plant and a cooling steam supply method for a gas turbine thereof wherein the temperature of cooling steam used as a cooling medium is appropriately adjusted so that the functional stability of the steam cooled system is not damaged. Therefore, the gas turbine can be made of an easily obtainable material.
In order to attain the object, a first embodiment hereof provides a combined cycle power plant comprising a combination of a gas turbine plant, a waste heat recovery boiler and a steam turbine plant. The gas turbine plant is constructed of a gas turbine, an air compressor driven by the gas turbine and a combustor for burning fuel together with compressed air supplied from said air compressor. The waste heat recovery boiler generates steam by using exhaust heat from the gas turbine as a heat source and is constructed of portions, mutually connected by pipings, of a high pressure steam generating portion, an intermediate pressure steam generating portion and a low pressure steam generating portion. The high pressure steam generating portion comprises a high pressure economizer, a high pressure feed water pump, a high pressure evaporator and a high pressure superheater. The intermediate pressure steam generating portion comprises an intermediate pressure economizer, an intermediate pressure feed water pump, an intermediate pressure evaporator and an intermediate pressure reheater. The low pressure steam generating portion comprises a low pressure economizer, a low pressure feed water pump, a low pressure evaporator and a low pressure superheater.
The steam turbine plant is constructed of steam turbines, mutually connected by piping, including a high pressure turbine, an intermediate pressure turbine and a low pressure turbine. The high pressure turbine is supplied with high pressure steam from the high pressure steam generating portion. The intermediate pressure turbine is supplied with intermediate pressure steam from the intermediate pressure steam generating portion, and the low pressure turbine is supplied with low pressure steam from the low pressure steam generating portion.
Steam supplied from the intermediate pressure evaporator is mixed into a cooling steam supply passage for supplying therethrough exhaust steam from the high pressure turbine as cooling steam into a high temperature portion of said gas turbine to be cooled.
That is, in the first embodiment, the exhaust steam from the high pressure turbine is first selected as the cooling medium of the gas turbine high temperature portion. Then, the intermediate pressure steam supplied from the intermediate pressure evaporator of the waste heat recovery boiler is mixed into the exhaust steam from the high pressure turbine. Thus, the cooling medium of a lowered temperature is made up and is supplied into the gas turbine high temperature portion for cooling thereof.
Thus, the high pressure exhaust steam, which is sufficient in volume, is mixed with the intermediate pressure steam, which is of a lower temperature but has a pressure nearly equal to that of the high pressure exhaust steam. Therefore, the high pressure exhaust steam is lowered in temperature and the high temperature portion to be cooled of the gas turbine can be made of a material of less heat resistant ability and a stable cooling can be effected without lowering of the entire efficiency.
Alternatively, the high pressure exhaust steam, which is sufficient in volume, may be mixed with a cooling water spray instead of the intermediate pressure steam. Therefore, the high pressure exhaust steam is appropriately lowered in temperature by the cooling water spray, so that the high temperature portion of the gas turbine is maintained at an appropriate temperature. As a result, the high temperature portion of the gas turbine which is to be cooled can be made of a material of less heat resistant ability, and a stable cooling can be effected without lowering of the entire efficiency of the power plant.
In other words, regardless of whether the intermediate pressure steam is mixed into the high pressure exhaust steam, the high pressure exhaust steam is mixed with the cooling water spray so as to be lowered in temperature anyway. Therefore, the intermediate pressure steam is stopped, and the cooling water spray is increased and mixed with the high pressure exhaust steam to be supplied into the high temperature portion of the gas turbine for cooling thereof. Thus, the steam from the intermediate pressure evaporator, which is available in less volume, is effectively supplied into the intermediate pressure turbine for work therein, and is effectively used for other necessary purposes. As a result, the steam is used more efficiently, and the efficiency of the combined plant is enhanced.
A second embodiment hereof includes a combined cycle power plant comprising a combination of a gas turbine plant, a waste heat recovery boiler and a steam turbine plant.
The gas turbine plant is constructed of a gas turbine, an air compressor driven by the gas turbine and a combustor for burning fuel together with compressed air supplied from the air compressor. The waste heat recovery boiler is for generating steam by using exhaust heat from the gas turbine as a heat source and is constructed of portions, mutually connected by pipings, of a high pressure steam generating portion, an intermediate pressure steam generating portion and a low pressure steam generating portion. The high pressure steam generating portion comprises a high pressure economizer, a high pressure feed water pump, a high pressure evaporator and a high pressure superheater. The intermediate pressure steam generating portion comprises an intermediate pressure economizer, an intermediate pressure feed water pump, an intermediate pressure evaporator and an intermediate pressure reheater. The low pressure steam generating portion comprises a low pressure economizer, a low pressure feed water pump, a low pressure evaporator and a low pressure superheater.
The steam turbine plant is constructed of steam turbines, mutually connected by pipings, of a high pressure turbine, an intermediate pressure turbine and a low pressure turbine. The high pressure turbine is supplied with high pressure steam from the high pressure steam generating portion. The intermediate pressure turbine is supplied with intermediate pressure steam from the intermediate pressure steam generating portion, and the low pressure turbine is supplied with low pressure steam from the low pressure steam generating portion.
A passage to be cooled by fuel from the gas turbine is provided to a cooling steam supply passage for supplying therethrough exhaust steam from the high pressure turbine as cooling steam into a high temperature portion of the gas turbine to be cooled.
That is, in the second embodiment, the exhaust steam from the high pressure turbine is first selected as the cooling medium of the gas turbine high temperature portion. Then, the exhaust steam is not directly used as the cooling steam to be supplied into the gas turbine high temperature portion, but is heat-exchanged with the gas turbine fuel to be lowered in temperature and then supplied into the gas turbine high temperature portion for cooling thereof.
A sufficient amount of the exhaust steam from the high pressure turbine is available as cooling steam, but this exhaust steam is also of a high temperature. Hence, it is heat-exchanged with the gas turbine fuel to be lowered in temperature, thereby the gas turbine high temperature portion to be cooled can be made of a material which is of a less heat resistant ability and yet a stable cooling can be effected without the entire efficiency being lowered.
A third embodiment hereof includes a combined cycle power plant comprising a combination of a gas turbine plant, a waste heat recovery boiler and a steam turbine plant. The gas turbine plant is constructed of a gas turbine, an air compressor driven by the gas turbine and a combustor for burning fuel together with compressed air supplied from the air compressor.
The waste heat recovery boiler is for generating steam by exhaust heat from the gas turbine as a heat source and is constructed of portions, mutually connected by pipings, of a high pressure steam generating portion, an intermediate pressure steam generating portion and a low pressure steam generating portion. The high pressure steam generating portion comprises a high pressure economizer, a high pressure feed water pump, a high pressure evaporator and a high pressure superheater. The intermediate pressure steam generating portion comprises an intermediate pressure economizer, an intermediate pressure feed water pump, an intermediate pressure evaporator and an intermediate pressure reheater. The low pressure steam generating portion comprises a low pressure economizer, a low pressure feed water pump, a low pressure evaporator and a low pressure superheater.
The steam turbine plant is constructed of steam turbines, mutually connected by pipings, of a high pressure turbine, an intermediate pressure turbine and a low pressure turbine. The high pressure turbine is supplied with high pressure steam from the high pressure steam generating portion. The intermediate pressure turbine is supplied with intermediate pressure steam from the intermediate pressure steam generating portion, and the low pressure turbine is supplied with low pressure steam from the low pressure steam generating portion.
A reheater is provided as a means for reheating steam which has cooled a high temperature portion of the gas turbine to be cooled.
That is, in the third invention, the construction is such that the steam which has cooled the gas turbine high temperature portion can be led into the reheater so as to be reheated there. Thus, even if the cooling steam after being used for cooling of the gas turbine is not high enough at a predetermined temperature because the gas turbine is not of a high enough temperature or the cooling has not been effected sufficiently or the like, then the cooling steam is reheated by the reheater and the necessary heat for the downstream steam turbines (such as the intermediate steam turbine) can be secured resulting in enhancement of the thermal efficiency.
A fourth embodiment here of includes a combined cycle power plant comprising a combination of a gas turbine plant, a waste heat recovery boiler and a steam turbine plant.
The gas turbine plant is constructed of a gas turbine, an air compressor driven by the gas turbine and a combustor for burning fuel together with compressed air supplied from the air compressor.
The waste heat recovery boiler is for generating steam by exhaust heat from the gas turbine as a heat source and is constructed of portions, mutually connected by pipings, of a high pressure steam generating portion, an intermediate pressure steam generating portion and a low pressure steam generating portion. The high pressure steam generating portion comprises a high pressure economizer, a high pressure feed water pump, a high pressure evaporator and a high pressure superheater. The intermediate pressure steam generating portion comprises an intermediate pressure economizer, an intermediate pressure feed water pump, an intermediate pressure evaporator and an intermediate pressure reheater. The low pressure steam generating portion comprises a low pressure economizer, a low pressure feed water pump, a low pressure evaporator and a low pressure superheater.
The steam turbine plant is constructed of steam turbines, mutually connected by pipings, of a high pressure turbine, an intermediate pressure turbine and a low pressure turbine. The high pressure turbine is supplied with high pressure steam from the high pressure steam generating portion, the intermediate pressure turbine is supplied with intermediate pressure steam from said intermediate pressure steam generating portion, and the low pressure turbine is supplied with low pressure steam from the low pressure steam generating portion.
A high pressure turbine by-pass passage is provided for connecting a superheated steam supply passage for supplying therethrough superheated steam from the high pressure superheater into the high pressure turbine, and a cooling steam supply passage for supplying therethrough exhaust steam from the high pressure turbine as cooling steam into a high temperature portion to be cooled of the gas turbine.
That is, according to the fourth embodiment, when the plant is to be started in accordance with operation procedures such as in WSS where the plant stops once a week, in DSS where the plant stop once a day or the like, the gas turbine is warmed up in advance by using the auxiliary boiler or its own compressed air. The initial steam generated by the boiler is supplied into the cooling steam passage of the gas turbine via the high pressure turbine by-pass passage, so that the warming-up is assisted so as to be accelerated.
When the boiler steam gets out of initial steam stage to start to be generated stably, the high pressure turbine by-pass passage is closed and the high pressure superheated steam is led into the high pressure turbine and the situation is changed gradually so that the cooling of the gas turbine is done by the high pressure exhaust steam from the high pressure turbine so that no thermal shock etc. is caused and the cooling of the gas turbine can be done stably.
A fifth embodiment hereof includes a cooling steam supply method in the combined cycle power plant as mentioned in the first invention. The gas turbine is supplied with the cooling steam as the combined cycle power plant is operated such that when the inlet temperature of the high pressure turbine is set to approximately 566xc2x0 C., the inlet pressure of the high pressure turbine is adjusted to 165 to 175 ata, and the exhaust steam from the high pressure turbine is maintained at a temperature of 330 to 250xc2x0 C. and a pressure of 35 to 30 ata.
That is, in the fifth embodiment, the inlet pressure of the high pressure turbine is adjusted to 165 to 175 ata. Therefore, the high pressure exhaust steam property is lowered to 330 to 250xc2x0 C. and 35 to 30 ata at the outlet of the high pressure turbine. Thus, the cooling steam can be lowered in temperature without the efficiency of the downstream equipment (the intermediate pressure turbine for example) being lowered. In addition, the downstream gas turbine high temperature portion to be cooled can be made of a material of less heat resistant ability and that is less expensive and yet a stable cooling can be effected without the entire efficiency being lowered.
A sixth embodiment hereof includes a cooling steam supply method in the combined cycle power plant as mentioned in any one of the first to fourth embodiments, characterized in that the high temperature portion of the gas turbine to be cooled is supplied with auxiliary steam prior to starting the gas turbine so that the gas turbine is warmed up. The auxiliary steam has the pressure of the combustion gas or greater at starting time of the gas turbine.
The gas turbine is then started in that state to do a holding operation for a predetermined time at a predetermined load. When steam from the waste heat recovery boiler comes to a condition of the auxiliary steam, the supply of the auxiliary steam is stopped and steam is supplied, by-passing the high pressure turbine, from the high pressure superheater of the waste heat recovery boiler into the high temperature portion of the gas turbine to be cooled.
When output of the waste heat recovery boiler comes to a rating thereof, the by-passing is closed and exhaust steam from the high pressure turbine is supplied into the high temperature portion of the gas turbine to be cooled so as to switch to a rated operation.
That is, in the sixth embodiment, when the plant is to be started in accordance with operational procedures such as in WSS where the plant stops once a week, in DSS where the plant stops once a day or the like, the cooling steam is supplied into the gas turbine portion to be cooled in the following procedures.
Firstly, the auxiliary steam at a pressure which is not less than that of the combustion gas effective at the starting time of the gas turbine is supplied into the gas turbine in advance of the starting thereof so that the gas turbine is warmed up. Then, the gas turbine is started so as to do a holding operation for a predetermined time at a predetermined load. The steam temperature and steam pressure of the waste heat recovery boiler are increased gradually, and when the steam condition of the waste heat recovery boiler comes to the steam condition of the auxiliary steam which has been used for the warming-up, the supply of auxiliary steam is stopped. The high pressure superheated steam which by-passes the high pressure turbine is then supplied into the gas turbine. When the output, or the steam condition, of the waste heat recovery boiler comes to a rating, the by-passing is closed so that the high pressure superheated steam is supplied into the high pressure turbine and the exhaust steam from the high pressure turbine is supplied into the gas turbine. Thus, the rated operation takes place.
A seventh embodiment hereof includes a cooling steam supply method in the combined cycle power plant as mentioned in any one of the first to fourth embodiments, characterized in that while the high temperature portion to be cooled of the gas turbine is closed upstream and downstream thereof, the gas turbine is started so as to do a holding operation for a predetermined time at a low load level which requires no cooling of the high temperature portion of the gas turbine.
When the waste heat recovery boiler comes to a level to generate a predetermined boiler steam, the closing is opened and steam is supplied, by-passing the high pressure turbine, from the high pressure superheater of the said waste heat recovery boiler into the high temperature portion of the gas turbine to be cooled.
When the output of the waste heat recovery boiler comes to a rating thereof, the by-passing is closed and exhaust steam from the high pressure turbine is supplied into the high temperature portion to be cooled of the gas turbine so as to switch to a rated operation.
That is, in the seventh embodiment, when the plant is to be started in accordance with operational procedures such as in WSS where the plant stops once a week, in DSS where the plant stops once a day or the like, the gas turbine portion to be cooled is first closed, by stop valves etc. for example, upstream and downstream thereof and the gas turbine is started. The gas turbine is held in the low load of approximately 20% load from no load which requires no cooling of the gas turbine portion to be cooled. When the boiler steam of the waste heat recovery boiler starts to be generated to reach a predetermined state of approximately 20 ata, for example, then the stop valves etc. are opened and the high pressure superheated steam, which by-passes the high pressure turbine, is supplied into the gas turbine portion to be cooled. When the gas turbine is further speeded up and the steam from the waste heat recovery boiler comes to a high temperature to reach what is called a rated state of 40 ata, for example, then the by-passing is closed and the high pressure exhaust steam from the high pressure turbine is supplied into the gas turbine portion to be cooled. Thus, the rated operation takes place.
An eighth embodiment hereof includes a combined cycle power plant as mentioned in any one of the first to fourth embodiments, characterized in that a dust collecting filter is provided at a cooling steam inlet portion of the high temperature portion of the gas turbine, and a mesh of the dust collecting filter is less than 1000 xcexcm and, specifically, in a range of 100 to 1000 xcexcm.
That is, in the eighth embodiment, the gas turbine is a recovery type steam cooled one, wherein there are provided cooling passages in the combustor, stationary blades and moving blades which are the high temperature portion of the gas turbine. The exhaust steam from the steam turbine is led into the cooling passages as the cooling steam. The dust collecting filter is provided at the cooling steam inlet portion of the gas turbine high temperature portion and the mesh thereof is less than 1000 xcexcm and, specifically, in the range of 100 to 1000 xcexcm. If the mesh is too small, fine particles contained in the steam may be caught, and clogging of the mesh is accelerated so as to make a long use thereof impossible so that frequent changes of the mesh are required. As the cooling steam temperature is usually a high temperature of 250xc2x0 C. or more, there is a difficulty in the exchange work of the mesh. But if the mesh is in the range of 100 to 1000 xcexcm, fine particles pass therethrough and these particles scarcely stay in the cooling steam passage with little possibility of accumulation therein because the cooling steam flows therein at a high velocity. Also, there is a case where solids of dropped scales such as iron oxide etc. in the main steam piping system flow into the cooling steam passage with a fear of blockage thereof, but the mesh is in the range of 100 to 1000 xcexcm so that the solids, being larger than the mesh usually, can mostly be removed by the mesh.
As mentioned above, according to the dust collecting filter, fine particles contained in the steam pass through the mesh and comparatively large solid particles only can be removed by the mesh. Thus, a long hour use of the mesh becomes possible and frequent exchange work of the mesh due to clogging becomes lessened.
Further, the dust collecting filter is provided in the cooling steam passage at the inlet portion of the gas turbine high temperature portion with a simple structure of the mesh portion being detachable. As a result, no large dust collecting device is needed and the system construction can be simplified.
A ninth embodiment hereof includes a combined cycle power plant as mentioned in any one of the first to fourth embodiments, characterized in that there are provided an impurity removing device which is exclusive for treating water for temperature adjustment, an economizer which is exclusive for heating the water from the impurity removing device and a spray nozzle for spraying the water heated at the economizer into cooling steam which flows into the high temperature portion of the gas turbine to be cooled. Therefore, the cooling steam temperature is adjusted.
That is, in the ninth embodiment, the gas turbine is a recovery type steam cooled one, wherein the cooling steam is led from the steam turbine system into the gas turbine high temperature portion for cooling thereof, and this cooling steam is returned to the steam turbine system for recovery. But there is sometimes a case where the temperature of the cooling steam is not appropriate for cooling of the gas turbine high temperature portion. As the gas turbine high temperature portion, there are stationary blades and moving blades, for example. The steam temperature which is appropriate for cooling of the stationary blades is higher than that appropriate for cooling of the moving blades. Hence, if the cooling steam is not of an appropriate temperature for cooling of the stationary blades, the cooling steam is required to be lowered in temperature. In this case, the temperature is adjusted by water being sprayed into the steam. In such case where the water is so sprayed, impurities are contained in the water which need to be removed. If the entire amount of the water which has been condensed is to be treated, then the facilities therefor become large and the cost therefor also increases.
Thus, in the present invention, the exclusive impurity removing device is provided which has a capacity only to treat the water amount necessary for adjusting the cooling steam temperature, and the exclusive economizer for heating only the water so treated at the impurity removing device. As the cooling steam is of a high temperature in the range of 250 to 600xc2x0 C., the water is heated at the economizer so that the temperature of that water is approached as near as possible to the cooling steam temperature. The high temperature water so heated at the economizer is sprayed into the cooling steam for adjustment of the temperature thereof.
According to the present invention, an exclusive impurity removing device of the capacity to only treat the amount of water necessary for adjusting the cooling steam temperature, and an exclusive economizer for heating only the water so treated at the impurity removing device are provided. Thus, the cooling steam temperature adjusting system can be compact-sized with no large facilities being needed, the feed water is heated to become the high temperature water of a temperature near the cooling steam temperature, and the adjustment of the cooling steam temperature can be done efficiently.